A magnetic random access memory (MRAMs) may provide non-volatile memory that can operate at relatively low voltage and at relatively high speed. In a magnetic random access memory cell, data is stored in a magnetic resistor including a magnetic tunneling junction (MTJ) element having first and second ferromagnetic layers and a tunneling insulating layer therebetween. More particularly, a magnetic polarization of the first ferromagnetic layer (also referred to as a free layer) may be changed using a magnetic field that crosses the MTJ element. The magnetic field may be induced by an electric current passing adjacent to the MTJ element.
Accordingly, the magnetic polarization of the free layer can be parallel or anti-parallel to a magnetic polarization of the second ferromagnetic layer (also referred to as a pinned layer). As a result of spintronics based on quantum mechanics, an electrical resistance of a current path through the MTJ element when the magnetic polarization of the free layer is parallel to the magnetic polarization of the pinned layer is different than an electrical resistance of the current path through the MTJ element when the magnetic polarization of the free layer is anti-parallel to the magnetic polarization of the pinned layer. A memory cell including an MTJ element can thus be programmed by setting the magnetic polarization of the free layer according to a value of the data to be programmed, and data can be read from the memory cell by measuring an electrical resistance through the MTJ element.
A magnetic tunneling junction element may include a pinning layer 11, a pinned magnetic layer 13, a tunneling insulating layer 15, and a free magnetic layer 17, as shown in FIGS. 1A–B. The pinning layer 11 may be a layer of an anti-ferromagnetic material such as FeMn (iron-manganese). The pinned and free magnetic layers 13 and 17 may be layers of the same or different ferromagnetic materials such as CoFe (cobalt-iron) and/or NiFe (nickel-iron). The tunneling insulating layer 15 may be a layer of an insulating material such as Al2O3 (aluminum oxide).
A ferromagnetic material has a macroscopic magnetization without an external magnetic field, and electron spins can be lined up in the same direction at a relatively low temperature. Magnetic regions of a ferromagnetic material may be aligned using an external magnetic field, and the alignment of the magnetic regions of the ferromagnetic material may be maintained after removing the external magnetic field. In an anti-ferromagnetic material, spins of atoms may be in an alternate anti-parallel arrangement. An anti-ferromagnetic material may thus have microscopic magnetic properties but not macroscopic magnetic properties.
The pinned magnetic layer 13 may be fixed by heating the pinned magnetic layer 13 to 300° C. (degrees C.) while applying an external magnetic field. After the heat treatment, the fixed magnetic spins in the pinned magnetic layer 13 may not rotate. Because the pinning layer 11 is in contact with the pinned layer 13, magnetic spins of the pinned layer 13 may be permanently fixed. Magnetic spins of the free layer 17, however, may rotate in the presence of an external magnetic field because the free layer 17 is separated from the pinning layer 11.
When the magnetic polarization of the free magnetic layer 17 is set parallel to the magnetic polarization of the pinned magnetic layer 13, an electrical resistance with respect to a current i through the magnetic tunneling junction element may be relatively low representing a “0” state of a bit of data programmed in the memory cell including the MTJ element. When the magnetic polarization of the free magnetic layer 17 is set anti-parallel to the magnetic polarization of the pinned magnetic layer 13, an electrical resistance with respect to a current i through the magnetic tunneling junction element may be relatively high representing a “1” state of a bit of data programmed in the memory cell including the MTJ element. By applying a same voltage across the MTJ element, a resulting current i may thus be relatively high or low due to a resistance of the MTJ element to indicate a state (“0” or “1”) of a bit of data programmed in the MTJ element.
Thermally assisted magnetic random access memories are discussed, for example, in U.S. Pat. No. 6,385,082, the disclosure of which is incorporated herein in its entirety by reference. In the '082 patent, a storage cell is disposed at an intersection of a bit line and a word line, and a cell can be selected using a brief pulse of tunneling current between the intersecting bit and word lines to provide sufficient Joule heating to facilitate a change in the magnetization state of its reversible magnetic layer.
In addition, thermally assisted switching of magnetic memory elements is discussed in U.S. Pat. No. 6,603,678, the disclosure of which is incorporated herein in its entirety by reference. In the '678 patent, a magnetic memory element is written to by heating the memory element and applying at least one magnetic field to the memory element.